It is estimated that a 6 GW of geothermal electricity capacity of the early 1990s should have approximately doubled by the year 2002. Moreover, technical advances in electricity production from geothermal sources should allow modest reductions in the unit cost energy. Today there are about 250 installations for producing electric power from geothermal energy. Geothermal power plants use steam produced from reservoirs of hot water placed a few kilometres below the earth’s surface with the purpose of activating a generator, which produce electricity. There are 4 main types of plants. The dry steam power plant, the single flash power plant, the binary cycle power plant and the lately developed double flash power plant.

The Hot Dry Rock (HDR) technology was developed during the 1970s aiming to provide thermal energy for electricity generation. Heat is extracted from artificial injection of cold water into crystalline plutonic rocks or metamorphic basement complexes. Despite technical difficulties the HDR prospects are encouraging during the last decade.